Mobile homes and modular housing units are frequently referred to as "manufactured housing." Unlike conventional housing units built on site, manufactured housing units are relatively tightly sealed; their window and door openings are relatively windproof and their walls relatively free from cracks and discontinuities of insulation, etc. This has given rise to various difficulties; their insulating materials, for example, may give off noxious fumes. Accumulation of moisture, particularly in attic spaces, is also a problem.
Recently enacted regulations of the Housing & Urban Development Administration require manufacturers to make supplemental ventilation systems available, as purchaser options. One of several such regulatory options is: "A fresh-air inlet (not for combustion air) which draws its air from the exterior of the home (not the underside) . . . " which" . . . shall be continuously connected from a forced-air furnace to the exterior and be capable of providing at least 25 cubic feet per minute with the furnace fan in normal operation."
Since any of such supplemental ventilation provisions is a mere buyer's option, furnace manufacturers have sought ways to provide such option without making a fundamental increase in the capacity of their furnace blowers. At least one manufacturer has therefore turned to the use of a supplemental blower which will also ventilate the attic space. This type of apparatus includes a forced-air inlet fan installed in the attic space. This fan draws air from the exterior and divides it into two portions. The first portion puts the attic space under positive pressure (thereby driving out moist air through a remote attic outlet); the second portion is driven through a duct leading through the ceiling, to the furnace's room air circulating blower.
This solution has not been found applicable to those downflow furnaces, such as electric furnaces, which are designed for the installation of air conditioner coils on substantially the entire upper surface of the furnace cabinet. More fundamentally and less obviously, such an installation overlooks the basic problem how to rid the room space of foul air, because it puts the attic space as well as the room space under positive air pressure, and thus effectively eliminates the attic space as an outlet for air from the room space.